Data Structures and Algorithms Practice MCQs

Question 1

What should be established first when solving a programming problem?

Accepted Answer

A. Inputs, outputs and constraints

Answer

Inputs, outputs and constraints

Answer

The programming language to use

Answer

The data structure to implement

Answer

The fastest known algorithm

Question 2

Which statement best defines an algorithm?

Accepted Answer

B. A finite, unambiguous procedure that solves a specified problem

Answer

Any Java source file that compiles without errors

Answer

A finite, unambiguous procedure that solves a specified problem

Answer

A data type defined only by its values and operations

Answer

A sequence of steps that may run forever on some valid inputs

Question 3

What does an abstract data type (ADT) specify?

Accepted Answer

D. Values and operations, independent of representation

Answer

The memory layout used to store the values

Answer

The Java class that implements the operations

Answer

The running time of each operation on one machine

Answer

Values and operations, independent of representation

Question 4

Which of the following is part of a stack ADT's behavioural contract rather than an implementation detail?

Accepted Answer

B. pop returns the most recently pushed remaining item

Answer

The items are kept in an array of capacity 100

Answer

pop returns the most recently pushed remaining item

Answer

The top index starts at -1 when the stack is empty

Answer

Each node links to the next node through a reference

Question 5

Binary search requires its input array to be sorted. In contract terms, "the array is sorted" is the operation's:

Accepted Answer

A. Precondition

Answer

Precondition

Answer

Postcondition

Answer

Loop invariant

Answer

Loop variant

Question 6

After push(x) completes, size() has grown by one and peek() returns x. In contract terms, these statements are push's:

Accepted Answer

C. Postcondition

Answer

Precondition

Answer

Loop invariant

Answer

Postcondition

Answer

Loop variant

Question 7

What is a loop invariant?

Accepted Answer

B. A property that holds before and after every iteration

Answer

A condition that becomes true only after the loop ends

Answer

A property that holds before and after every iteration

Answer

A quantity that strictly decreases on every iteration

Answer

A condition that must be false for the loop to start

Question 8

Which three steps make up a loop-invariant proof of correctness?

Accepted Answer

B. Initialization, preservation and termination

Answer

Declaration, compilation and execution

Answer

Initialization, preservation and termination

Answer

Input, processing and output

Answer

Base case, recursive case and return

Question 9

To prove that a loop always terminates, what is typically shown?

Accepted Answer

D. A nonnegative integer measure decreases every iteration

Answer

The loop invariant holds before the first iteration

Answer

The loop body contains no nested loop

Answer

The loop gives correct output on sample tests

Answer

A nonnegative integer measure decreases every iteration

Question 10

A student's maximum method starts with best = 0 and replaces best whenever a[i] > best. For which input does it return a wrong answer?

Accepted Answer

D. [-8, -3, -10]

Answer

[3, 18, 11]

Answer

[0, 15, -2]

Answer

[7, -7, 7]

Answer

[-8, -3, -10]

Question 11

For a nonempty int array a, which initialization of best makes the maximum algorithm correct for every input?

Accepted Answer

C. best = a[0]

Answer

best = 0

Answer

best = -1

Answer

best = a[0]

Answer

best = a.length

Question 12

What happens when this Java method is called with an empty array?

```
static int max(int[] a) { int best = a[0]; for (int i = 1; i < a.length; i++) if (a[i] > best) best = a[i]; return best; }
```

Accepted Answer

B. It throws ArrayIndexOutOfBoundsException

Answer

It returns 0 for the empty array

Answer

It throws ArrayIndexOutOfBoundsException

Answer

It throws NullPointerException

Answer

It returns Integer.MIN_VALUE

Question 13

A text-analysis program is split into separate tokenizing, word-counting and report-formatting components, each with its own inputs and outputs. Which technique is this?

Accepted Answer

A. Decomposition

Answer

Decomposition

Answer

Encapsulation

Answer

Memoization

Answer

Backtracking

Question 14

Which group contains only nonlinear data structures?

Accepted Answer

C. Tree, heap, graph

Answer

Array, stack, queue

Answer

Linked list, stack, deque

Answer

Tree, heap, graph

Answer

Array, linked list, tree

Question 15

Why should an array-based stack class keep its items array and top field private?

Accepted Answer

D. So that clients cannot break its internal invariant

Answer

So that push and pop run in O(1) time

Answer

So that the stack can store any object type

Answer

So that the array never needs to grow

Answer

So that clients cannot break its internal invariant

Data Structures and Algorithms Practice MCQs

Data Structures and Algorithms Free MCQs

What should be established first when solving a programming problem?

Which statement best defines an algorithm?

What does an abstract data type (ADT) specify?

Which of the following is part of a stack ADT's behavioural contract rather than an implementation detail?

Binary search requires its input array to be sorted. In contract terms, "the array is sorted" is the operation's:

After push(x) completes, size() has grown by one and peek() returns x. In contract terms, these statements are push's:

What is a loop invariant?

Which three steps make up a loop-invariant proof of correctness?

To prove that a loop always terminates, what is typically shown?

A student's maximum method starts with best = 0 and replaces best whenever a[i] > best. For which input does it return a wrong answer?

For a nonempty int array a, which initialization of best makes the maximum algorithm correct for every input?

What happens when this Java method is called with an empty array? ``` static int max(int[] a) { int best = a[0]; for (int i = 1; i < a.length; i++) if (a[i] > best) best = a[i]; return best; } ```

A text-analysis program is split into separate tokenizing, word-counting and report-formatting components, each with its own inputs and outputs. Which technique is this?

Which group contains only nonlinear data structures?

Why should an array-based stack class keep its items array and top field private?

A stack ADT is implemented once with an array and once with linked nodes. Which statement is true?

A sorting method passes 50 hand-picked test cases. What can be concluded?

A linear search is written with the loop for (int i = 0; i < a.length - 1; i++). Which test case exposes the bug?

The maximum algorithm starts with best = a[0] and loops for i = 1 to n - 1. For a = [4, 9, 2, 11, 5], what is best just before the iteration with i = 3?

Which three basic control constructs are sufficient to express any algorithm?

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